The figures are in plain sight, so that anyone desiring to know the value of any point on the curve can look above the point to get the actual figure wanted, without having to read from the scale at the left-hand edge and then estimate roughly the value for any point which happens to fall in a space between two horizontal lines of the scale. Reading from the figures at the top of the chart permits any desired figure to be obtained more rapidly and much more accurately. In addition to this, the figures are recorded in such manner that they may be quoted for use elsewhere by anyone who may wish to make use of the data in a speech or in a written article in which the chart itself cannot be used.

It would be a desirable thing if in all curve charts the figures for the horizontal scale were placed at the bottom of the chart rather than at the top. Many illustrations in this book, taken from pubhcations of excellent standing, show dates (such as years, months, etc.) at the top of the chart. If the horizontal scale were always placed at the bottom, the standard arrangement would be a convenience to the reader and would give the additional advantage that the top of the

CURVE PLOTTING

y

/^

/

^

y

>

y^

lOOO

^^

y

"^

chart would be free for a numerical statement such as is found at the top of Fig. 68.